Toxoplasma gondii is a ubiquitous intracellular protozoan parasite that is a common infection in AIDS patients and other immunocompromised individuals as well as the cause congenital toxoplasmosis. In AIDS patients and other immunocompromised hosts infection is due to reactivation of a latent infection in the brain that results in a severe and often fatal necrotizing encephalitis. Cytokines play an important role in the regulation of T. gondii in the central nervous system. Interferon-gamma (IFNgamma) is the main cytokine controlling replication of T. gondii in the brain. My previous studies defined that IFN-gamma significantly inhibits the replication of T. gondii in astrocytes. The mechanism of IFNgamma in astrocytes was found to be independent of all of the known anti-Toxoplasma effector mechanisms. However, we recently determined that IFN? mediated inhibition in astrocytes was reversed in astrocytes deficient in the GTP binding protein, IGTP (AIGTP). The function of IGTP is not known but it is thought to be involved in regulation of the vesicular trafficking pathway. Preliminary microarray studies of IFNgamma induced gene expression in astrocytes indicate that host cell cholesterol metabolism is altered in IFNgamma treated astrocytes. T. gondii has recently been shown to require cholesterol uptake from the host cell. Effects on lipid and cholesterol trafficking to the parasitophorous vacuole may be the mechanism of IFNgamma inhibition in astrocytes. As IFNgamma dependent mechanism(s) play a major role in controlling T. gondii in the brain, understanding these mechanism(s) remains an important challenge in understanding disease pathogenesis. In this project the mechanism(s) of IFNgamma induced inhibition in astrocytes will be investigated. The specific aims of this proposal are: 1) To perform a microarray analysis of IFNgamma response genes in wildtype vs. IGTP knockout (deltaIGTP) astrocytes and 2) Investigate the hypothesis that IFNgamma affects vesicular trafficking to the parasitophorous vacuole (Aim 2A) or that IFNgamma affects cholesterol trafficking to the parasitophorous vacuole (Aim 2B) and that IGTP is involved in regulating this trafficking .